(1) Field of the Invention
The invention relates to a rotor drive system, particularly a rotor drive system of a tail rotor of a helicopter with the features of the preamble of claim 1.
In order to balance the reactive torque of a main rotor, it is known to provide helicopters with a tail rotor, driven and located in a duct, i.e. in a so called fenestron.
(2) Description of Related Art
Rotating thrust systems with blades controlled by a variable rotational speed instead of a variable pitch rate suffer of the problems of high torque moments and low thrust change rates, especially in the area of low rotational velocities. On the other side, thrust systems with a constant rotational speed and variable pitch often cannot lower the rotational speed or change the direction of rotation.
The document US 2009/140095 A1 discloses a rotary-wing aircraft with an electric motor mounted along an axis of rotation to drive a rotor system about the axis of rotation.
The document WO 02/096752 A1 discloses an electro-magnetic drive system arranged within a hub area and having a frictionless/non-contacting electromagnetic support of rotor blades.
The document JP 2011006041 discloses an electrical tail rotor with motor located in a hub having rotary blades.
Individual blade pitch control of turbines in wind farms is known from the document US 2012/0051907.
The document US 2006/049304 A1 discloses a hover aircraft with an air impeller engine having an air channel duct and a rotor with outer ends of its blades fixed to an annular impeller disk that is driven by magnetic induction elements arrayed in the air channel duct. The air-impeller engine is arranged vertically in the aircraft frame to provide vertical thrust for vertical take-off and landing. The air-impeller engine employs dual, coaxial, contra-rotating rotors for increased thrust and gyroscopic stability. An air vane assembly directs a portion of the air thrust output at a desired angle to provide a horizontal thrust component for flight manoeuvring or translation movement. Electric power is supplied to the magnetic induction drives by high-capacity lightweight batteries or fuel cells.
According to the document WO 2009/129309 A2 a wind generator is disclosed in which superconducting ring generators are utilized without the need for a load bearing drive shaft and other mechanical components.
The document GB 2360752 A discloses a ducted fan arrangement used for a helicopter's torque correction, with a variable blade pitch control. The pitch control of the fan is realized by a hard coupling to the main rotors collective control. An electrical generator in the ducted fan supplies current to the helicopter's electrical control and distribution system.
The document U.S. Pat. No. 4,953,811 A discloses a helicopter with an electrical powered tail rotor in a shroud. At least one permanent magnet energized synchronous motor with an increased pole number drives the tail rotor. Said at least one synchronous motor is integrated as a torus around an opening of the shroud encompassing the tail rotor. Blades of the tail rotor are fixed to at least one rotating component.
Until now, the anti-torque thrust system of helicopters is usually operating at a constant rotational speed and the change in thrust is usually generated by a variable rotor blade pitch. A thrust system where a change of thrust is generated by changing the blade pitch has several advantages compared to a thrust system where the rotational speed is changed. The change in thrust can be set very fast, just limited by the pitch change rate of the blades while the thrust change by a change in rotational speed is usually much slower due to the required acceleration and deceleration of the rotor. A thrust change by variable pitch causes just low changes in the torque of the rotational axis in contrast to a thrust change by a variable rotational speed, where the whole rotor mass needs to be accelerated, leading to a high rotor torque. This is not just of advantage for the power requirement of the driving system, but also for the moment equilibrium of a helicopter or any other system where the thrust system is built in. A thrust system which combines the two features, variable rotational speed and variable pitch is usually more complex because in addition to a drive which allows a variable rotational speed, also a system for changing the pitch needs to be built in. This increased complexity makes such a concept more expensive and heavy.